1. Field of the Invention
This invention relates to ribozymes that cleave RNA, and more specifically to the enhancement of ribozyme catalytic activity using facilitator oligonucleotides complementary to an RNA sequence contiguous to the ribozyme.
2. Description of the Related Art
Catalytic RNA, or "ribozymes" consist of a catalytic core having flanking sequences adjacent to the core that hybridize to the substrate RNA. The simplest catalytic core is an RNA motif known as a hammerhead. Since the discovery of RNA catalysts (ribozymes) by Cech, there has been a desire to design ribozymes to cleave viral or messenger RNA with high specificity and at a rapid rate. Historically, these requirements have been mutually limiting.
Ribozyme specificity depends on the number of base pairs formed between the ribozyme flanking sequences and its RNA substrate. Goodchild and Kohli studied the cleavage of a sequence from HIV-1 RNA by various hammerhead ribozymes. Increased base pairing has been shown to decrease the rate of cleavage. Goodchild and Kohli, Arch. Biochem. Biophys. 284, 386 (1991). They found that shorter flanking sequences resulted in weaker binding between the ribozyme and the cleavage products together with increased rate of cleavage. A ribozyme with 12 base flanking sequences cleaved 10 times faster then one with 20 bases.
However, to have the requisite selectivity or specificity, i.e., the ability to discriminate among all RNA molecules in a cell, a ribozyme must form a minimum of about 15 base pairs with the target substrate. This requirement for selectivity limits the rate of cleavage that may be realized.
Accordingly, ribozymes having increased catalytic activity or methods of increasing ribozyme catalytic activity are needed.